Lateral wellbores extend from a main wellbore. Multilateral wells may have a number of lateral wellbores extending from immediately adjacent main wellbores. A lateral wellbore forms a juncture with the main wellbore from which it extends. Generally, lateral wellbores are accessed through a window removed from the main wellbore wall. Sometimes the window opening is preformed in the casing and the lateral is drilled therethrough and extends therefrom and sometimes the window is formed entirely by drilling out from the main wellbore through the casing and cement, if any, through the borehole wall and outward therefrom. As shown in FIG. 1, a lateral 10 extends at an acute angle from a main wellbore 12. Since wellbores are generally formed to have circular cross sections, the window 14 often is elliptical or tear-drop, as shown, in shape having a substantially V-shaped downhole end 14a and a more rounded upper limit 14b at the upper end 16 of the lateral wellbore.
While the main wellbore is shown cased with casing 15 and including annular cement 17, the wellbore could be open hole without a lining of casing or cement. In such a case, the window would be the transition from the main wellbore wall to the wall of the lateral wellbore.
If it is desired to line the lateral wellbore with a liner, it is sometimes difficult to accurately position the liner relative to the window and, therefore, often the uphole end of the liner is positioned at a distance from the window along the lateral wellbore. This leaves an open hole region of the wellbore between the window and the liner. This open hole region can degenerate and possibly even cave in, especially when wellbore operations begin. Some solutions connect a flange to the upper end of the liner such that the flange can be fitted against the window in the main wellbore to position the liner. However, the flange remains protruded into the main wellbore and may adversely affect access therepast.